Prior to the assembly of a hard disc drive it is necessary for the disc to be cleaned so as to prevent unnecessary damage and increase the longevity of the assembled device.
On completion of the cleaning process, the disc must be rinsed so as to remove any stray particles that may have adhered to the disc.
Given the high volume of discs to be cleaned and rinsed during the manufacturing process, the cleaning and rinsing steps are performed in continuous or batch process lots and so pass through phase flow tanks prior to final assembly. As a result, the rinsing medium, such as water, will retain in suspension particles from previous batches within the phase flow tank. It is therefore necessary for the phase flow tank to have a continual replacement of the rinsing medium in order to remove the suspended particles and so avoid cross contamination with subsequent batches.
It has been found that for phase flow tanks, whilst removing a substantial proportion of the particles in suspension, there tends to be “dead zones” within the tank through eddies and other features of discontinuous turbulent flow leading to the retention of particles within the phase flow tank.
It is therefore necessary to frequently change the rinsing medium within the phase flow tank to avoid cross contamination. This can result in significant wastage of the rinsing medium as well as lost capacity in having the phase flow tank taken offline during replacement of the rinsing medium.